Great progress has been made in the field of hip replacements. Considering that hip replacements may not have even existed a generation ago, hip replacements are now relatively common in younger as well as older patients. In spite of the considerable progress which has been made, hip replacement instrumentation can be imprecise.
For example, an acetabular component is provided for the femoral head in a patient and for providing for a stable rotational and angular movement of the ball in the socket in accordance with the movements of the patient's leg. The acetabular component includes a cup which has to be disposed in an inclined and horizontally tilted relationship in the patient's pelvis. If the cup is not disposed in a proper relationship to the bony acetabulum, the femoral head will become displaced from the cup (hip dislocation) when the patient moves his or her leg about the cup as a fulcrum. This is often painful and incapacitating and can require the hip replacement operation to be repeated. Since the operation and the subsequent recovery are long, expensive and painful and carry significant medical and surgical risks, a repeat of a hip replacement operation is not to be taken lightly.
Until now, the proper disposition of the acetabular component within the bony acetabulum for a proper rotational movement of the ball and socket joint has been relatively imprecise. In most instances, orthopedic surgeons have held an instrument (holding the cup) for positioning the cup and have judged on an eyeball basis the initial positioning of the instrument and the manual rotation of the instrument in each of two (2) coordinate directions in an attempt to position the cup properly relative to the acetabulum.
More recently, computer guidance in association with pre-operative magnetic resonance imaging (MRI and computed tomography (CT), and/or x-ray techniques have been employed to assist in determining the coordinates through which the cup has had to be moved to be oriented in a proper relationship to the pelvis. Such techniques have been costly and labor intensive, particularly since the determinations made as by magnetic resonance techniques have had to be registered in the operating room by time consuming point Verification to connect the operative bony anatomy to the pre-operative image data. The application of these techniques by using such imaging studies in the operating room have added substantial time and cost to the operative procedure and have raised a question as to the true value of such techniques. As a result, any initial advantage provided by such techniques such as the magnetic resonance imaging or computed tomography outside of the operating room have been nullified.
As a result of the imprecise instrumentation now being provided to position a cup and femoral component properly relative to the pelvis and bony acetabulum and femur, approximately 2 to 10% of hip replacement operations have suffered the complication of dislocation as a result of component malpositioning. Considering that hip replacement operations are painful and expensive and the recovery can be lengthy and painful, full recovery from a hip replacement operation usually requires months until the recovery can be considered to be at all complete. Rigid exercise schedules during the period of recovery have often had to be imposed.
In a hip replacement operation, certain trial components are utilized prior to placing the actual prosthesis. For example, the ball (femoral head) disposed at the top of the femur and providing the rotational relationship with the socket in the acetabulum is replaced by a metal ball. Furthermore, a liner made from a suitable plastic having low frictional characteristics is disposed on the acetabulum to receive the metal ball. These removals, replacements and insertions affect the length of the patient's leg receiving the hip replacement. If the length of this leg does not match the length of the patient's other leg, the patient will walk with a limp. Techniques to match the length of the leg receiving the hip replacement to the length of the other leg have not been entirely satisfactory.
When attempts have been made to match the length of the patient's leg receiving the hip replacement to the length of the patient's other leg, the position of the center of the cup has become offset from its optimum position. This can affect the ability of the femur ball to rotate in the acetabulum socket and can also affect the ease with which the rotation occurs. This problem has not been satisfactorily addressed in the prior art.